This invention relates generally to high resistivity films and coatings, and more particularly relates to high resistivity chromium silicide films and coatings deposited by sputtering. 2. Description of the Prior Art
High resistivity coatings that are chemically and physically stable over a wide range of temperatures are useful in a number of applications. Such coatings can be used, for example, in impedance matching applications as well as in the fabrication of resistive elements in thin film integrated circuit structures. In addition to high resistivity, in the aforementioned applications, it is also desirable to provide films which (1) can withstand the chemicals and high temperatures used in integrated circuit fabrication processes and other fabrication processes and (2) can be deposited in such a way as to minimize cracking and delamination. In addition, in many applications it is important that the films be electrically stable, that is, they exhibit constant resistivities even after prolonged heating as may occur in use or in processing.
To this end, several attempts have been made at providing stable, high resistivity films and coatings. Early attempts involved sputter deposition of tantalum nitride, copper-germanium alloys and Nichrome (an alloy containing nickel, chromium and iron; "Nichrome" is a trademark of Driver-Harris Co., Harrison, N.J. While coatings of sufficient thickness to eliminate problems with cracking and delamination have been prepared by sputter deposition of these materials and are in fact useful in some applications, the relatively low rsistivity obtained in each case is a limiting factor for many other applications. With Nichrome, for example, coherent films are stable only up to about 200 ohms per square.
The method of this invention provides films of much higher resistivity than previously obtained, even at thicknesses on the order of several thousand angstroms, which films are also chemically, physically, and electrically stable over a wide range of temperatures. The films are deposited by reactive sputtering of a CrSi.sub.2 target. While a large number of patents disclose the use of magnetron sputtering in the formation of various types of films and coatings, we are not aware of any that teach or suggest a process for forming temperature-stable high resistivity films. As representative examples:
U.S. Pat. No. 4,513,905 to Nowicki et al. shows a process for sputter depositing a protecting, "barrier" layer of chromium or titanium on a layer of silicon. The process involves reactive sputtering in a partial atmosphere of nitrogen.
U.S. Pat. No. 4,461,799 to Gavrilov et al., in the context of providing wear-resistant coatings on cutting tools, discloses successively depositing on an aluminum oxide or ceramic base (1) a pure metal and (2) a carbide or nitride of titanium or zirconium.
U.S. Pat. No. 3,257,305 to Varga discloses the use of sputtering to form tantalum oxide coatings on semiconductor substrates.
U.S. Pat. No. 4,131,530 to Blum et al. discloses a method of sputter depositing a crack-resistant coating on a plastic substrate. The target is primarily comprised of chromium and iron. The primary advantage of the process, in the context of providing automobile trim, is stated to be the improved resistance to sunlight and water.
U.S. Pat. No. 4,337,990 to Fan et al. shows a transparent thermal barrier formed from composite films. In a preferred embodiment, titanium oxide is sputter deposited on either side of a metallic silver film.
U.S. Pat. No. 4,219,608 to Nishiyama et al. discloses high resistivity piezoelectric crystalline films made by sputtering zinc oxide and sulfur, selenium or tellurium. The process is directed to the issue of obtaining a particular crystalline orientation within the piezoelectric films.
U.S. Pat. No. 4,252,865 to Gilbert et al. discloses a solar-energy device having a sputter-deposited coating of an amorphous semiconductor material such as germanium.
U.S. Pat. No. 4,113,599 to Gillery shows sputter deposition of indium oxide, tin oxide, or indiumtin oxide films on glass. The sputtering is reactive is that it is carried out in the presence of oxygen gas.
U.S. Pat. 3,574,143 to Vratny discloses preparation of a "resistive composition" by sputtering hafnium compounds in the presence of nitrogen.